P29. developing a long-term survival hemi-facial vascularized composite allotransplantation swine model to study facial nerve regeneration

PURPOSE: We present a survival large animal model for preclinical facial transplant research to evaluate facial nerve regeneration. METHODS: 19 survival surgeries (16 auto-transplant, 3 allotransplant) were performed to develop and validate a hemi-facial composite flap based on the external carotid artery and vein. Assessment of nerve regeneration using serial compound muscle action potentials (CMAP), electroneurograms (ENG) and histology in a 3-4 month survival model was established. Immunosuppression in allotransplanted pigs started on POD-3 and maintained with weight-based Cyclosporin (CSA) (target levels of 200-300), mycophenolic acid and prednisone. Postoperative course and complications were documented. RESULTS: The buccal branch was selected to assess nerve regeneration using nerve conduction studies. In our allotransplant and auto-transplant models, minor wound breakdown and sialoceles in early postoperative period were managed conservatively or with superficial debridement. There were no flap losses. No systemic infections were experienced in the allotransplanted pigs (n=3); one pig developed an abscess requiring debridements, extended antibiotics usage, but had complete resolution at 8 weeks. At 3 months nerve regeneration reached 75% distance to target muscle with comparable ENG to normal side in auto-transplanted Sinclair mini-pig group (n=5), but a slower rate of regeneration in the allotransplanted group (n=3). CONCLUSION: This study demonstrates proof of concept for an allotransplant large experimental animal model for research to inform post-surgical care to improve facial nerve regeneration and functional outcomes.